Cardiopulmonary bypass vascular catheters, for example, left atrial or left heart vent and left ventricular vent catheters, are used to drain fluid from the left ventricle to prevent excessive pressure build-up in the left heart portion during bypass surgery. The left atrial vent catheter may be inserted through the right superior pulmonary vein, left atrium, and mitral valve, and into the left ventricle. The left ventricular vent catheter may be introduced directly into the left ventricle through the ventricle wall. After insertion, the stylet is removed from the catheter and the catheter is connected to the extracorporeal system that includes artificial heart and lung apparatus.
Many such catheters have been made of polyvinyl chloride (PVC) and with a rigid plastic stylet or a malleable wire imbedded in a sidewall of the catheter. However, since heart surgery is now being performed at relatively low temperatures, conventional PVC catheters have become less desirable because they become relatively rigid and less flexible at the lower temperatures making the catheter more difficult to manipulate during insertion and removal from the patient. Also, with relatively stiff catheters there is greater risk of damage to the heart during the operation. For this reason, such catheters have more recently been made of silicone rubber which is soft and supple, and these characteristics are substantially not affected by the low temperatures encountered during surgery. Because silicone rubber catheters are soft and supple, there is less chance of damage to the patient during insertion and removal of the catheter as well as during the operation.
If the diameter of the stylet is excessively small, it may kink and bend excessively relative to the catheter making the manual preshaping of the catheter less accurate or controllable. Stylets have been formed of closely coiled stainless steel wire so that the stylet has a substantially larger diameter than that of the straight wire in order to more nearly fill the catheter lumen. In this way, the stylet can have a sufficiently large diameter relative to the catheter lumen so as to produce a catheter having sufficiently good handling and shaping characteristics, and yet have a high malleability due to the small size of wire used in the coiled stylet. However, coiled stainless steel wire stylets are relatively heavy and expensive compared to straight wire stylets. Catheters having a malleable wire embedded in the sidewall of the catheter have been used to allow shaping of the catheter prior to insertion but the suppleness or flexibility of such catheters while in the heart and vessels of the patient are limited by the presence of the wire which cannot be removed from the catheter. Non-malleable plastic such as nylon or high density polyethylene rods have been proposed as stiffeners but are generally limited to catheters that do not require manual preshaping.